Formerly, inboard marine propulsion devices employing horizontally mounted engines had their motor supports or bases secured directly to the hull of the boat. The motor supports were usually attached at four or more points to the boat. As a result, much of the vibration and noise generated in the engines and propulsion devices was transmitted to the boat with consequent unpleasant effects. This problem was partially addressed by the development of three point mounting systems. These three point mounting systems were instrumental in helping to isolate engine vibration.
However, three point systems have not fully solved the problem of engine vibration. Furthermore, to date, a mount has not been developed which is sufficiently soft to absorb engine vibration at idle, while being sufficiently stiff to support additive loads and vibrations when a horizontal thrust propulsion load is present.
In prior art systems it is commonly known to mount the marine engine on a three point suspension assembly, the assembly being disposed about the engine roll axis, to support the engine with respect to the stringers. Rubber isolators are commonly provided at each suspension point to absorb vibration of the engine.
Generally, in the prior art, the marine gear is mounted to the engine by means of a drive shaft. The marine gear is connected to the propeller shaft, and moves generally independently of the engine. Accordingly, the thrust of the propeller is absorbed by the marine gear mounting system. However, new packaging designs have required that the marine gear be mounted to and move with the marine engine. In this configuration, the marine engine and marine gear assembly are subject to the thrust forces from the propeller which were previously absorbed by the marine gear mounting system.
A unique problem occurs when a thrust load is imposed directly upon the engine. Even where resilient grommets or sleeves have been provided around mounting bolts to prevent direct contact thereof with the frame or engine, such mounts are unsatisfactory. The high thrust loads from the propeller shaft caused rapid deterioration of such grommets resulting in early failure. This deterioration permits direct metal-to-metal contact and direct transmission of vibration and sound from the engine support structure to the hull of the boat. Such sound and vibrations travel throughout the ship's hull and can become magnified. Such vibrations can have a detrimental effect of the ship's structure and equipment. In addition, vibrations within the audible range can be disturbing to passengers.
Accordingly, it would be desirable to develop an engine mounting system which would absorb the horizontal propeller thrust forces while simultaneously providing sufficient vertical support to the engine to support the engine weight and compensate for engine roll due to torque. Presently, no such mounting system is available which absorbs horizontal thrust and vertical vibration within a single mounting bracket housing.
Accordingly, an object of the present invention is develop a marine engine and marine gear mounting system which solves the above mentioned problems faced by the prior art systems.
A further object of the present invention is to provide a single mounting bracket which is capable of absorbing horizontal thrust loads and vertical engine loads simultaneously.
Accordingly, the present invention provides a vibration absorbing assembly for mounting a marine engine to a stringer, comprising: a mounting bracket adapted for attachment to the marine engine; a base adapted for attachment to the stringer; and first and second resilient vibration absorbing members supported within the mounting bracket and selectively connected to said base, the first resilient member being relatively more yieldable in a horizontal direction for cushioning horizontal thrust loads acting upon the bracket with respect to said base, the first resilient member providing substantially zero resistance to vertical movement of the bracket with respect to said base when no horizontal thrust load is acting upon the bracket with respect to said base, and the second resilient member being relatively more yieldable in a vertical direction for cushioning vertical loads upon the bracket with respect to said base.
Also provided is a vibration isolating system for a marine engine and drive gear assembly to be mounted upon a pair of longitudinally extending, generally parallel stringers, comprising: a trunnion mount for mounting the front of the engine to the crossmember; and a pair of vibration absorbing assemblies, each assembly configured for mounting the rear of the engine and marine gear to the respective stringer, each assembly including: a mounting bracket adapted for attachment to the engine; a base adapted for attachment to a stringer and first and second resilient vibration absorbing members supported within the mounting bracket and selectively connected to said base, the first resilient member being relatively more yieldable in a horizontal direction for cushioning horizontal thrust loads acting upon the bracket with respect to said base, the first resilient member providing substantially zero resistance to vertical movement of the bracket with respect to said base when no horizontal thrust load is acting upon the bracket with respect to said base, and the second resilient member being relatively more yieldable in a vertical direction for cushioning vertical loads upon the bracket with respect to said base.